The present invention relates to a vacuum power interrupter, and more particularly to an arc-shield supporting structure of a vacuum power interrupter.
In an vacuum power interrupter, an arc is produced between electrical contacts at the time when the contacts are closed and thereby an electric current flows or at the time when the contacts are opened and thereby the electric current flow is interrupted, whereby metal particles from the electrical contact are scattered.
In order to shield such scattering metal particles a vacuum power interrupter is provided with a metal shield member so as to surround the electrical contacts. This makes it possible to freeze and solidify them onto the surface of the shield member, thereby to prevent a deterioration of insulation at the inner wall of the insulating vessel. Since the shield member is required to make an electric potential level within an interrupter uniform and maintain good insulation, it is necessary to dispose the shield member symmetrically with respect to stationary and movable electric contacts and support it on the inner surface of the vacuum vessel so that its electric potential becomes floating level. Moreover, since a large impact force is applied to the shield member when interrupting an electric current, it is necessary to constitute the shield member so that it can effectively relax this impact force and has durable construction while being free from play or swing.
Reference is made to prior art arc-shield supporting structure of a vacuum power interrupter. A method of making the supporting structure comprises the steps of stacking two small size containers each having a tubular flange formed at the axial ends of two small containers stacked, interposing the shield member therebetween, and joining them by means of brazing to form a vacuum vessel.
Since it is necessary to use a metal fitting for supporting the shield member, a creeping distance for maintaining insulation is substantially reduced. As a result, it is necessary to elongate the insulating tube so as to guarantee the creeping distance, resulting in enlarging the size of the vacuum power interrupter. In the prior art vacuum power interrupter fabricated by stacking two vacuum containers, the number of connecting portions increases. Further, in the above construction the shield member is supported at the connecting portion, resulting in an increase of the number of connecting plates and welding step, and a requirement of high skill in welding technique. Another drawback is that the number of assembly steps are increased, resulting in low work efficiency.